This invention relates generally to the design and control of engineering systems. Across a broad range of industries, modern engineering systems are characterized by marked increases in complexity and simultaneous decreases in component tolerances. As a result, engineering control systems are subject to greater operational demands, which require more sophisticated and detailed modeling techniques.
Fluid-based engineering systems provide a range of relevant examples. These include gas turbine engines for aviation and power generation, HVAC&R (heating, ventilation, air-conditioning and refrigeration), fuel cells, and other, more generalized fluid processing systems for hydrocarbon extraction, materials processing, and manufacture. These systems contain any or all of the following components: turbo-machinery, fuel cell stacks, electric motors, pipes, ducts, valves, mixers, nozzles, heat exchangers, gears, chemical apparatuses and other devices for generating or modifying a fluid flow.
Each of these applications places different operational demands on the engineering control system. In gas turbine engines, for example, the relevant cycle is typically a Brayton turbine or first Ericsson cycle, and the basic thermodynamic parameters (or process variables) are the pressure, temperature and flow rate of the working fluid at the inlet, compressor, combustor, turbine, and exhaust. The parameters are related to the overall thrust, rotational energy, or other measure of power output. In order to precisely control this output while maintaining safe, reliable and efficient engine operation, the engineering control system should be fast, accurate and robust, and provide real-time control capability across a range of performance levels. While the relevant process variables vary depending on the system type and configuration, the need for precise, efficient and reliable engineering control remains the same, as do the economic constraints on overall cost and operational/maintenance requirements.
In the particular areas of turbine flow path analysis and clearance control, heat transfer between turbine components and the working fluid is an important aspect of system behavior. Specifically, tip clearance is related to heat transfer via the relative thermal expansion of adjacent turbine components, for example rotor and blade assemblies as compared to a turbine case or compressor housing, and stationary vanes as compared to a rotating shaft or hub.
With respect to flow path modeling and analysis, the relevant parameters are the pressure ratio, temperature and other flow parameters, as defined for a particular flow stream through a particular flow area (e.g., a fixed or variable nozzle area for working fluid flow, a bleed valve, or a fixed or variable-area orifice for cooling fluid flow). Existing models typically treat the complex phenomena of heat transfer and clearance separately, using independent sets of temperature and thermal growth states, and applying different analysis methods to operational states and calibration data. Existing flow parameter models, on the other hand, are often unstable under low-flow and choked-flow conditions. A more integrated and physics-based approach increases reliability and fidelity of these models, providing more efficient turbine system control over a wider range of conditions.